The conjunction それに is often treated as a single vocabulary item, but it is actually formed from two distinct parts: the pronoun それ ('that') and the case marking particle に.

In this structure, それ refers to the entire statement that came just before it. The particle に then functions to attach a new, related piece of information. This combination effectively means 'to that' or 'on top of that', where 'that' is the previous sentence. It is most commonly translated as 'what's more', 'on top of that', or 'furthermore'.

• それに、この部屋(へや)は家賃(やちん)が高(たか)すぎるんじゃない？
  On top of that, isn't the rent for this room too expensive?
• 佐藤(さとう)さんは仕事(しごと)ができる。それに性格(せいかく)もいい。
  Sato-san is good at his job. What's more, he has a great personality.

Because それに uses the particle に to build upon the prior information, the new information must share the same general sentiment. In other words, それに should connect two positive statements or two negative statements, but never a mix of both.

• テスト(てすと)で百点(ひゃくてん)を取(と)り、それに先生(せんせい)に褒(ほ)められた！
  I got a perfect score on the test, and on top of that, the teacher praised me! (Natural Japanese, as both events are positive)
• 財布(さいふ)をなくしたし、それに終電(しゅうでん)にも乗(の)り遅(おく)れて、とても困(こま)った。
  I lost my wallet, and in addition to that, I missed the last train. I was in a real bind. (Natural Japanese, as both events are negative)
• 映画(えいが)は楽(たの)しかった。それに帰(かえ)りに頭(あたま)が痛(いた)くなった。
  The movie was fun. Furthermore, I got a headache on the way home. (Unnatural Japanese, as one event is positive, while the other is negative)